The significance of polymicrobial growth in urine: contamination or true infection.

Urine growing more than one organism is usually considered contaminated. During 1980-1984, among 198 episodes of urosepsis with at least one identical organism in blood and urine, there were 62 with polymicrobial growth from urine. The significance of the multiple growth from urine was confirmed in 12 episodes by the growth of more than one identical organism in blood and urine and in 21 episodes by repeated growth of the same mixture of organisms in multiple urine specimens. Escherichia coli had a higher tendency to invade blood stream than other Gram-negative organisms, such as pseudomonas and proteus. In specific populations with high risk of polymicrobial infection, multiple growth in urine should be carefully evaluated with appropriate colony count and identification of each isolate.